Variable fluidic waveguide attenuator

ABSTRACT

A waveguide attenuator apparatus ( 100 ) includes a variable waveguide attenuator ( 102 ) having at least one waveguide attenuator cavity ( 109 ) and a fluidic dielectric ( 108 ) having a loss tangent, a permittivity and a permeability at least partially disposed within the waveguide attenuator cavity. At least one composition processor ( 101 ) is included and adapted for dynamically changing a composition or volume of the fluidic dielectric to vary the loss tangent, the permittivity and/or the permeability. A controller ( 136 ) is provided for controlling the composition processor to selectively vary the loss tangent, the permittivity and/or the permeability in response to a waveguide attenuator control signal ( 137 ). In one arrangement, the permittivity and permeability can be varied concurrently.

BACKGROUND OF THE INVENTION

1. Statement of the Technical Field

The inventive arrangements relate generally to methods and apparatus forproviding increased design flexibility for RF circuits, and moreparticularly to a waveguide attenuator.

2. Description of the Related Art

A waveguide typically includes a material medium that confines andguides a propagating electromagnetic wave. In the microwave regime, awaveguide normally consists of a hollow metallic conductor, usuallyrectangular, elliptical, or circular in cross section. This type ofwaveguide may, under certain conditions, contain a solid or gaseousdielectric material.

In a waveguide or cavity, a “mode” is one of the various possiblepatterns of propagating or standing electromagnetic fields. Each mode ischaracterized by frequency, polarization, electric field strength, andmagnetic field strength. The electromagnetic field pattern of a modedepends on the frequency, refractive indices or dielectric constants,and waveguide or cavity geometry.

An “evanescent field” in a waveguide is a time-varying field having anamplitude that decreases monotonically as a function of transverseradial distance from the waveguide, but without an accompanying phaseshift. The evanescent field is coupled, i.e., bound, to anelectromagnetic wave or mode propagating inside the waveguide.

Variable waveguide attenuators are commonly used to attenuate microwavesignals propagating within a waveguide, which is a type of transmissionline structure commonly used for microwave signals. Waveguides typicallyconsist of a hollow tube made of an electrically conductive material,for example copper, brass, steel, etc. Further, waveguides can beprovided in a variety of shapes, but most as previously mentioned oftenare cylindrical or have a rectangular cross section. In operation,waveguides propagate modes above a certain cutoff frequency.

Waveguide attenuators are available in a variety of arrangements. In onearrangement, the waveguide attenuator consists of three sections ofwaveguide in tandem: a middle section and two end sections. In eachsection a resistive film is placed across an inner diameter of thewaveguide (in the case of a waveguide having a circular cross section)or across a width of the waveguide (in the case of a waveguide having arectangular cross section). In either case, the resistive filmcollinearly extends the length of each waveguide section. The middlesection of the waveguide is free to rotate radially with respect to thewaveguide end sections. When the resistive film in the three sectionsare aligned, the E-field of the an applied microwave signal is normal toall films. When this occurs, no current flows in the films and noattenuation occurs. When the center section is rotated at an angle θwith respect to the end section at the input of the waveguide, the Efield can be considered to split into two orthogonal components, E sin θand E cos θ. E sin θ is in the plane of the film and E cos θ isorthogonal to the film. Accordingly, the E sin θ component is absorbedby the film and the E cos θ component is passed unattenuated to the endsection at the output of the waveguide. The resistive film in the endsection at the output then absorbs the E cos θ sin θ component of the Efield and an E cos² θ component emerges from the waveguide at the sameorientation as the original wave. The accuracy of such an attenuator isdependant on the stability of the resistive films. If the resistivefilms should degrade over time, performance of the waveguide attenuatorwill be affected. Further, energy reflections and higher-order modepropagation commonly occur in such a waveguide attenuator design.

In another arrangement, a wedge shaped waveguide attenuator havingresistive surfaces exists. Because the waveguide attenuator is wedgeshaped, the E field again can be considered to split into two orthogonalcomponents at each surface of the wedge, E sin θ and E cos θ. As withthe previous example, the E sin θ component of a microwave signal isabsorbed by the film. However, The tapered portion of the waveguideattenuator causes energy reflections to occur. Hence, the wedge shapedwaveguide attenuator must be long enough to obtain sufficiently lowreflection characteristics. Accordingly, this type of waveguideattenuator is limited to use in relatively long waveguides. Thus, a needexists for a waveguide attenuator that provides additional designflexibility and overcomes the limitations described above with respectto existing waveguide attenuators.

SUMMARY OF THE INVENTION

The present invention relates to a variable waveguide attenuator. Thevariable waveguide attenuator includes at least one waveguide attenuatorcavity and a fluidic dielectric having a loss tangent, a permittivityand a permeability at least partially disposed within the waveguideattenuator cavity. At least one composition processor is included andadapted for changing a composition or a volume of the fluidic dielectricto vary the loss tangent, the permittivity and/or the permeability. Acontroller is provided for controlling the composition processor toselectively vary the volume, shape, loss tangent, the permittivityand/or the permeability in response to a waveguide attenuator controlsignal. In one arrangement, the permittivity and permeability can bevaried concurrently.

The composition processor can selectively vary the volume and/or losstangent to vary the attenuation of the continuously variable waveguideattenuator. The composition processor also can selectively vary thepermeability and/or volume to maintain the characteristic impedanceapproximately constant when at least one of the loss tangent and thepermittivity is varied. Further, the composition processor canselectively vary the permittivity and/or volume to maintain thecharacteristic impedance approximately constant when at least one of theloss tangent and the permeability is varied. Further, the permittivityand/or the permeability can be adjusted to adjust the characteristicimpedance.

A plurality of component parts can be dynamically mixed together in thecomposition processor in response to the waveguide attenuator controlsignal to form the fluidic dielectric. The composition processor caninclude at least one proportional valve, at least one mixing pump, andat least one conduit for selectively mixing and communicating aplurality of the components of the fluidic dielectric from respectivefluid reservoirs to a waveguide attenuator cavity. The compositionprocessor can further include a component part separator adapted forseparating the component parts of the fluidic dielectric for subsequentreuse.

The component parts can be selected from the group consisting of (a) alow permittivity, low permeability, low loss component, (b) a highpermittivity, low permeability, low loss component, and (c) a highpermittivity, high permeability, high loss component. In anotherarrangement, the component parts can be selected from the groupconsisting of (a) a low permittivity, low permeability, low losscomponent, (b) a high permittivity, low permeability, low losscomponent, (c) a high permittivity, high permeability, low losscomponent, and (d) a low permittivity, low permeability, high losscomponent. The fluidic dielectric can include an industrial solventwhich can have a suspension of magnetic particles contained therein. Themagnetic particles can consist of ferrite, metallic salts, andorgano-metallic particles. In one arrangement, variable waveguideattenuator can contain about 50% to 90% magnetic particles by weight.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram useful for understanding the variablewaveguide attenuator of the present invention.

FIG. 2 is a block diagram of another variable waveguide attenuator inaccordance with the present invention.

FIG. 3 is a block diagram of yet another variable waveguide attenuatorhaving an alternate shape.

FIG. 4 is a flow chart that is useful for understanding the process ofthe invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides the circuit designer with an added levelof flexibility by permitting a fluidic dielectric to be used in awaveguide attenuator, thereby enabling attenuation and impedancecharacteristics of the waveguide attenuator to be varied. For example,either dielectric particles or fluids having a high loss tangent can bemixed into a fluid dielectric having a low to moderate loss tangent andthe mixture ratio can be adjusted to vary the attenuation. Several highloss dielectric fluids exist. Examples are the Ferrotec EMG series,specifically EMG805, EMG807 and EMG1111. Examples of lossy particlesinclude ferrite powder and cobalt powder, both available in micron-sizedparticles suitable for use in suspensions. Lossy fluids such as theaforementioned Ferrotec liquids would probably be a better choice asthey are more likely to form a homogeneous mix as opposed to a particlesuspension of Fe or Co. Further, the composition of the fluidicdielectric can be adjusted to change the impedance of the waveguideattenuator or to maintain a constant impedance as the particle densityis adjusted. For example, the impedance of the waveguide attenuator canbe precisely matched to the impedance of a waveguide by maintaining aconstant ratio of ∈_(r)/μ_(r), where ∈_(r) is the relative permittivityof the fluidic dielectric, and μ_(r) is the relative permeability of thefluidic dielectric. A precisely matched impedance can minimize energyreflections caused by a transition from an unattenuated portion of thewaveguide to the waveguide attenuator. A precisely matched impedancealso-reduces higher-order mode propagation. The volume and/or shape ofthe waveguide attenuator can also be adjusted using fluidics. In otherwords, a dielectric fluid can be used to alter the electrical size whilea conductive fluid could be used alter the physical size or shape of thewaveguide attenuator to provide tunable cut-off frequencies,attenuators, filters as well as mode control or suppression.

FIG. 1 is a conceptual diagram that is useful for understanding thevariable waveguide attenuator apparatus 100 of the present invention.The attenuator apparatus 100 can vary the characteristics of thewaveguide attenuator 102, which comprises an attenuator cavity region109 contained within a waveguide 104. The cavity region 109 is filledwith a fluidic dielectric 108 to vary attenuation characteristics,permittivity and/or permeability of the waveguide attenuator 102 byeither varying the composition or volume of fluidic dielectric withinthe cavity region 109. The waveguide 104 can be any structure capable ofsupporting propagation modes. Waveguides are commonly embodied aselectrically conductive tubes having circular or rectangular crosssections, but the present invention is not so limited; the presentinvention can be incorporated into any type of waveguide having anydesired shape. For example, the present invention can be incorporatedinto a waveguide comprising circuit traces on a dielectric substrate anda plurality of rows of conductive vias which cooperatively supportpropagation modes. In such an example, at least one cavity forcontaining fluidic dielectric can be positioned between adjacent rows ofconductive vias. Additional vias having one end which couples to thecavity can be provided as a pathway for the flow of fluidic dielectricin and out of the cavity.

The waveguide attenuator 102 can be located anywhere within thewaveguide 104. For example, the waveguide attenuator 102 can be locatedin a central location within the waveguide 104 at either end of thewaveguide 104, or anywhere in between. Further, multiple waveguideattenuator cavities (see FIG. 2 and 3) can be included in a singlewaveguide, for instance to provide an option of cascading waveguidefilters within the waveguide 104. In one arrangement, successivecavities can be filled with dielectric fluid to achieve levels ofattenuation higher than might be achieved by merely varying the fluidicdielectric in a single cavity. For example, a plurality of waveguideattenuator cavities each providing a range of attenuation levels ofapproximately 0-10 dB can be provided. Experimental data from a recentstudy found that in a coplanar waveguide transmission line structure(not to be confused with a conventional waveguide) the fluids providedan increased loss of between 2 and 20 dB of loss per inch oftransmission line. Loss could be adjusted by both changes in the fluidas well as change in length of the waveguide section. If 18 dB ofattenuation is needed, the attenuation of two waveguide filter cavitiescan be adjusted to be 9 dB. Alternatively, a first waveguide attenuatorcavity can be adjusted to provide 10 dB of attenuation while the secondwaveguide attenuator cavity is adjusted to provide 8 dB of attenuation.Still, a myriad of combinations of waveguide filter cavities andattenuation levels can be used, any of which are within the scope of thepresent invention.

Although the shape of the waveguide attenuator 102 is primarilycontrolled by the shape of the cavity region 109, the waveguideattenuator 102 can incorporate other objects which protrude within thecavity 109. For example, tuning screws can protrude into the cavityregion 109 to vary RF propagation characteristics within the cavity.Further, the cavity region 109 can comprise adjustable barriers and/orother objects which can change the RF response of the waveguideattenuator 102. Likewise, the control of volume within the cavity region109 or regions can also alter the response of the waveguide attenuator.In particular, changing the dimensions and/or volume of fluid within thecavity region 109 can change the frequency of modes supported withincavity region 109.

Notably, the waveguide attenuator 102 can be provided in a variety ofshapes. For example, the waveguide attenuator can be bounded on foursides by the walls 105 of the waveguide 104 and bounded on two sides bybarriers 106. Preferably, the barriers are made of a dielectric materialso as not to disrupt waveguide performance. In other arrangements thecavity 109 can be arranged in more complex shapes, for example a wedgeshape.

A wedge shape, as shown in FIG. 3, can be particularly useful tominimize reflection of an RF signal 220 due to the waveguide attenuator202, for example, when there is an impedance mismatch between thewaveguide attenuator 202 and the remaining dielectric 222 within awaveguide 204. Such an impedance mismatch can occur when the waveguideattenuator 202 has a different characteristic impedance than theremaining dielectric 222. The waveguide attenuator 202 can be positionedwith a narrow end 208 oriented towards an end 212 of the waveguide 204receiving RF input 220 and a wide end 210 of the waveguide attenuator202 towards an output end 214 of the waveguide 204. Since there is alarge angle of incidence between the RF signal 220 and a diagonalbarrier 216, very little signal energy will be reflected towards theinput end 212. Further, since the depth of the waveguide cavity 206varies along the length of the waveguide attenuator 202, the amount oflossy fluidic dielectric existing within subcavities or chambers 251,252, 253, and 254 between opposing waveguide walls 224 and 226 willvary. Accordingly, the attenuation of the waveguide attenuator 202 willvary over its' length. The change in attenuation should be taken intoconsideration when computing the overall net attenuation of thewaveguide attenuator 202. A controller 201 containing look-up tables forcontrolling a pump 203 or multiple pumps as well as a reservoir orreservoirs in conjunction with valves 134 can shift volumes of fluidicdielectric to and from the subcavities or chambers via correspondinginput conduits 261, 262, 263, and 264 and output conduits 271, 272, 273,and 274. Note that chambers or subcavities 251-254 vary in volume andthat the present invention is not limited to a particular number ofcavities. The greater the number of cavities in this regard the more“fine tuning” that will be available.

Referring again to FIG. 1, a composition processor 101 is provided forchanging a composition or volume of the fluidic dielectric 108 to varythe attenuation characteristics of the fluidic dielectric. Further, itis preferable that the composition processor 101 also change thecomposition of the fluidic dielectric 108 to vary permittivity and/orpermeability in order to maintain control over the characteristicimpedance of the waveguide attenuator 102. A controller 136 controls thecomposition processor for selectively varying the attenuation,permittivity and/or permeability of the fluidic dielectric 108 inresponse to a waveguide attenuator control signal 137 on control inputline 138. By selectively varying the attenuation, permittivity and/orpermeability of the fluidic dielectric, the controller 136 can controlattenuation of an RF signal, for example a microwave signal, through thewaveguide 104 as well as group velocity of the RF signal. Further, thecontroller 136 can control the impedance of the waveguide 104 within thecavity region 109.

Composition of Fluidic Dielectric

The fluidic dielectric can be comprised of several component parts thatcan be mixed together to produce a desired attenuation, permittivity andpermeability required for particular waveguide attenuatorcharacteristics. In this regard, it will be readily appreciated thatfluid miscibility and particle suspension are key considerations toensure proper mixing. Another key consideration is the relative ease bywhich the component parts can be subsequently separated from oneanother. The ability to separate the component parts is important whenthe attenuation or impedance requirements change. Specifically, thisfeature ensures that the component parts can be subsequently re-mixed ina different proportion to form a new fluidic dielectric.

It may be desirable in many instances to select component mixtures thatproduce a fluidic dielectric that has a relatively constant responseover a broad range of frequencies. If the fluidic dielectric is notrelatively constant over a broad range of frequencies, thecharacteristics of the fluid at various frequencies can be accounted forwhen the fluidic dielectric is mixed. For example, a table of losstangent, permittivity and permeability values vs. frequency can bestored in the controller 136 for reference during the mixing process.

Aside from the foregoing constraints, there are relatively few limits onthe range of component parts that can be used to form the fluidicdielectric. Accordingly, those skilled in the art will recognize thatthe examples of component parts, mixing methods, volume distributionmethods, and separation methods as shall be disclosed herein are merelyby way of example and are not intended to limit in any way the scope ofthe invention. Also, the component materials are described herein asbeing mixed in order to produce the fluidic dielectric. However, itshould be noted that the invention is not so limited. Instead, it shouldbe recognized that the composition of the fluidic dielectric could bemodified in other ways. For example, the component parts could beselected to chemically react with one another in such a way as toproduce the fluidic dielectric with the desired values of permittivityand/or permeability. All such techniques will be understood to beincluded to the extent that it is stated that the composition or volumeof the fluidic dielectric is changed.

A nominal value of permittivity (∈_(r)) for fluids is approximately 2.0.However, the component parts for the fluidic dielectric can includefluids with extreme values of permittivity. Consequently, a mixture ofsuch component parts can be used to produce a wide range of intermediatepermittivity values. For example, component fluids could be selectedwith permittivity values of approximately 2.0 and about 58 to produce afluidic dielectric with a permittivity anywhere within that range aftermixing. Dielectric particle suspensions can also be used to increasepermittivity and loss tangent.

According to a preferred embodiment, the component parts of the fluidicdielectric can be selected to include (a) a low permittivity, lowpermeability, low loss component and (b) a high permittivity, highpermeability, high loss component. These two components can be mixed asneeded for increasing the loss tangent while maintaining a relativelyconstant ratio of permittivity to permeability. A third component partof the fluidic dielectric can include (c) a high permittivity, lowpermeability, low loss component for allowing adjustment of thepermittivity of the fluidic dielectric independent of the permeability.Still, a myriad of other component mixtures can be used. For example,the following fluidic dielectric components can be provided: (a) a lowpermittivity, low permeability, low loss component, (b) a highpermittivity, low permeability, low loss component, (c) a highpermittivity, high permeability low loss component, and (d) a lowpermittivity, low permeability, high loss component.

Several high loss dielectric fluids exist. Examples are the Ferrotec EMGseries, specifically EMG805, EMG807 and EMG1111. Lossy fluids such asthe aforementioned Ferrotec liquids would probably be a better choice asthey are more likely to form a homogeneous mix as opposed to a particlesuspension of Fe or Co.

High levels of magnetic permeability are commonly observed in magneticmetals such as Fe and Co. For example, solid alloys of these materialscan exhibit levels of μ_(r) in excess of one thousand. By comparison,the permeability of fluids is nominally about 1.0 and they generally donot exhibit high levels of permeability. However, high permeability canbe achieved in a fluid by introducing metal particles/elements to thefluid. For example typical magnetic fluids comprise suspensions offerro-magnetic particles in a conventional industrial solvent such aswater, toluene, mineral oil, silicone, and so on. Other types ofmagnetic particles include metallic salts, organo-metallic compounds,and other derivatives, although Fe and Co particles are most common. Thesize of the magnetic particles found in such systems is known to vary tosome extent. However, particles sizes in the range of 1 nm to 20 μm arecommon. The composition of particles can be varied as necessary toachieve the required range of permeability in the final mixed fluidicdielectric after mixing. However, magnetic fluid compositions aretypically between about 50% to 90% particles by weight. Increasing thenumber of particles will generally increase the permeability.

An example of a set of component parts that could be used to produce afluidic dielectric as described herein would include oil (lowpermittivity, low permeability and low loss), a solvent (highpermittivity, low permeability and low loss), and a magnetic fluid, suchas combination of an oil and a ferrite (low permittivity, highpermeability and high loss). Further, certain ferrofluids also can beused to introduce a high loss tangent into the fluidic dielectric, forexample those commercially available from FerroTec Corporation ofNashua, N.H. 03060. In particular, Ferrotec part numbers EMG0805,EMG0807, and EMG1111 can be used. An example of a relatively lowdielectric fluid with moderate to high loss is Lord MRF-132AD whichexhibits a dielectric constant between 5 and 6 and a loss ofapproximately 5-6 times that of air. A hydrocarbon dielectric oil suchas Vacuum Pump Oil MSDS-12602 could be used to realize a lowpermittivity, low permeability, and low loss tangent fluid. A lowpermittivity, high permeability fluid may be realized by mixing thehydrocarbon fluid with magnetic particles or metal powders which aredesigned for use in ferrofluids and magnetoresrictive (MR) fluids. Forexample magnetite magnetic particles can be used. Magnetite is alsocommercially available from FerroTec Corporation. An exemplary metalpowder that can be used is iron-nickel, which can be provided by LordCorporation of Cary, N.C. Fluids containing electrically conductivemagnetic particles require a mix ratio low enough to ensure that noelectrical path can be created in the mixture. Additional ingredientssuch as surfactants can be included to promote uniform dispersion of theparticles. High permittivity can be achieved by incorporating solventssuch as formamide, which inherently posses a relatively highpermittivity. Fluid Permittivity also can be increased by adding highpermittivity powders such as Barium Titanate manufactured by FerroCorporation of Cleveland, Ohio. For broadband applications, the fluidswould not have significant resonances over the frequency band ofinterest.

Processing of Fluidic Dielectric For Mixing/Unmixing of Components

The composition processor 101 can be comprised of a plurality of fluidreservoirs containing component parts of fluidic dielectric 108. Thesecan include: a first fluid reservoir 122 for a low permittivity, lowpermeability component of the fluidic dielectric; a second fluidreservoir 124 for a high permittivity, low permeability component of thefluidic dielectric; a third fluid reservoir 126 for a high permittivity,high permeability, high loss component of the fluidic dielectric. Thoseskilled in the art will appreciate that other combinations of componentparts may also be suitable and the invention is not intended to belimited to the specific combination of component parts described herein.For example, the third fluid reservoir 126 can contain a highpermittivity, high permeability, low loss component of the fluidicdielectric and a fourth fluid reservoir can be provided to contain acomponent of the fluidic dielectric having a high loss tangent.

A cooperating set of proportional valves 134, mixing pumps 120, 121, andconnecting conduits 135 can be provided as shown in FIG. 1 forselectively mixing and communicating the components of the fluidicdielectric 108 from the fluid reservoirs 122, 124, 126 to cavity 109.The composition processor also serves to separate out the componentparts of fluidic dielectric 108 so that they can be subsequently re-usedto form the fluidic dielectric with different attenuation, permittivityand/or permeability values. All of the various operating functions ofthe composition processor can be controlled by controller 136. Theoperation of the composition processor shall now be described in greaterdetail with reference to FIG. 1 and the flowchart shown in FIG. 4.

The process can begin in step 302 of FIG. 4, with controller 136checking to see if an updated waveguide attenuator control signal 137has been received on an attenuator input line 138. If so, then thecontroller 136 continues on to step 304 to determine an updated losstangent value for producing the attenuation indicated by the waveguideattenuator control signal 137. The updated loss tangent value necessaryfor achieving the indicated attenuation can be determined using alook-up table.

In step 306, the controller can determine an updated permittivity valuefor matching the characteristic impedance indicated by the waveguideattenuator control signal 137. For example, the controller 136 candetermine the permeability of the fluidic components based upon thefluidic component mix ratios and determine an amount of permittivitythat is necessary to achieve the indicated impedance for the determinedpermeability.

Referring to step 308, the controller 136 causes the compositionprocessor 101 to begin mixing two or more component parts in aproportion to form fluidic dielectric that has the updated loss tangentand permittivity values determined earlier. Alternatively or inconjunction with mixing, the composition processor 101 can also beginaltering specified volumes of fluidic dielectric to or from one or morecavities, subcavities or chambers within the waveguide attenuator tocompensate for the previously determined updated values. In the casethat the high loss component part also provides a substantial portion ofthe permeability in the fluidic dielectric, the permeability will be afunction of the amount of high loss component part that is required toachieve a specific attenuation. However, in the case that a separatehigh permeability fluid is provided as a high permeability componentpart, the permeability can be determined independently of the losstangent. This mixing process and/or volume shifting can be accomplishedby any suitable means. For example, in FIG. 1 a set of proportionalvalves 134 and mixing pump 120 are used to mix component parts fromreservoirs 122, 124, 126 appropriate to achieve the desired updated losstangent, permittivity and permeability values.

In step 310, the controller causes the newly mixed fluidic dielectric108 to be circulated into the cavity 109 through a second mixing pump121 . In step 312, the controller checks one or more sensors 116, 118 todetermine if the fluidic dielectric being circulated through the cavity109 has the proper values of loss tangent, permittivity and permeabilityor to determine proper volumes corresponding to the previouslydetermined updated values. Sensors 116 are preferably inductive typesensors capable of measuring permeability. Sensors 118 are preferablycapacitive type sensors capable of measuring permittivity. Further,sensors 116 and 118 can be used in conjunction to measure loss tangent.The loss tangent is the ratio at any particular frequency between thereal and imaginary parts of the impedance, and the impedance can bedetermined from resistance (R), conductance (G), inductance (L) andcapacitance (C) measurements. Additionally, loss tangent can be easilycalculated using a separate resonator device, such as a dielectric ringresonator. Such cavity resonator devices are commonly used to computethe quality factor, Q, from which loss tangent is easily extracted. Thesensors can be located as shown, at the input to mixing pump 121.Sensors 116, 118 are also preferably positioned to measure the losstangent, permittivity and permeability of the fluidic dielectric passingthrough input conduit 113 and output conduit 114. Note that it isdesirable to have a second set of sensors 116, 118 at or near the cavity109 so that the controller can determine when the fluidic dielectricwith updated loss tangent, permittivity and permeability values hascompletely replaced any previously used fluidic dielectric that may havebeen present in the cavity 109.

In a system based on mixtures rather then volumes of static compositionsof fluid, step 314 optionally involves having the controller 136comparing the measured loss tangent to the desired updated loss tangentvalue determined in step 304. If the fluidic dielectric does not havethe proper updated loss tangent value, the controller 136 can causeadditional amounts of high loss tangent component part to be added tothe mix from reservoir 126, as shown in step 315.

If the fluidic dielectric is determined to have the proper level of lossin step 314, then the process continues on to optional step 316 wherethe measured permittivity from step 312 is compared to the desiredupdated permittivity value determined in step 306. If the updatedpermittivity value has not been achieved, then high or low permittivitycomponent parts are added as necessary, as shown in step 317. The systemcan continue circulating the fluidic dielectric through the cavity 109until both the loss tangent and permittivity passing into and out of thecavity 109 (or the volume of a specific fluidic dielectric) are theproper value, as shown in step 318. Once the loss tangent andpermittivity are the proper value, the process can continue to step 302to wait for the next updated waveguide attenuator control signal.

Significantly, when updated fluidic dielectric is required, any existingfluidic dielectric must be circulated out of the cavity 109. Anyexisting fluidic dielectric not having the proper loss tangent and/orpermittivity can be deposited in a collection reservoir 128. The fluidicdielectric deposited in the collection reservoir can thereafter bere-used directly as a fourth fluid by mixing with the first, second andthird fluids or separated out into its component parts so that it may bere-used at a later time to produce additional fluidic dielectric. Theaforementioned approach includes a method for sensing the properties ofthe collected fluid mixture to allow the fluid processor toappropriately mix the desired composition, and thereby, allowing areduced volume of separation processing to be required. For example, thecomponent parts can be selected to include a first fluid made of a highpermittivity solvent completely miscible with a second fluid made of alow permittivity oil that has a significantly different boiling point. Athird fluid component can be comprised of a ferrite particle suspensionin a low permittivity oil identical to the first fluid such that thefirst and second fluids do not form azeotropes. Given the foregoing, thefollowing process may be used to separate the component parts.

A first stage separation process would utilize distillation system 130to selectively remove the first fluid from the mixture by the controlledapplication of heat thereby evaporating the first fluid, transportingthe gas phase to a physically separate condensing surface whosetemperature is maintained below the boiling point of the first fluid,and collecting the liquid condensate for transfer to the first fluidreservoir. A second stage process would introduce the mixture, free ofthe first fluid, into a chamber 132 that includes an electromagnet thatcan be selectively energized to attract and hold the paramagneticparticles while allowing the pure second fluid to pass which is thendiverted to the second fluid reservoir. Upon de-energizing theelectromagnet, the third fluid would be recovered by allowing thepreviously trapped magnetic particles to combine with the fluid exitingthe first stage which is then diverted to the third fluid reservoir.

Those skilled in the art will recognize that the specific process usedto separate the component parts from one another will depend largelyupon the properties of materials that are selected and the invention.Accordingly, the invention is not intended to be limited to theparticular process outlined above.

The embodiments of FIGS. 2 and 3 illustrate alternative embodiments. Awaveguide attenuator apparatus 200 of FIG. 2 in particular illustrates asingle system using both mixture or composition control as well volumecontrol. In this instance, a similar controller 136 and compositionprocessor 101 as described with respect to FIG. 1 controls thecomposition of fluidic dielectric in a waveguide attenuator region 103of waveguide 104. Control signal 137 on control input line 138 controlsthe mixture and/or volume of fluidic dielectric via input conduit 113and output conduit 114 within the chamber or cavity defined betweenwalls 106 and 107. Likewise, another waveguide attenuator region 111defined between walls 107 and 117 includes a plurality of chambers orsubcavities 151, 152, and 153. Preferably, these cavities can be aplurality of capillary tubes having a plurality of corresponding inputconduits 161, 162 and 162 feeding fluidic dielectric to the cavities anda plurality of output conduits 171, 172, and 173 providing a means forremoving fluidic dielectric from the cavities. The volume control of thefluidic dielectric through the cavities, subcavities or chambers can beachieved cooperatively using a series of valves 134, a controller 201for controlling a pump 203 (or pumps) and optional reservoir orreservoirs as shown.

While the preferred embodiments of the invention have been illustratedand described, it will be clear that the invention is not so limited.Numerous modifications, changes, variations, substitutions andequivalents will occur to those skilled in the art without departingfrom the spirit and scope of the present invention as described in theclaims.

1. A variable waveguide attenuator, comprising: at least one waveguideattenuator cavity; a fluidic dielectric at least partially disposedwithin at least one subcavity within said waveguide attenuator cavity,said fluidic dielectric having a loss tangent, a permittivity and apermeability; at least one composition processor adapted for changing atleast one among an electrical characteristic and a physicalcharacteristic of the variable waveguide attenuator by manipulating saidfluidic dielectric to vary at least one of a volume, said loss tangent,said permittivity and said permeability of the fluidic dielectric; and acontroller for controlling said composition processor in response to awaveguide attenuator control signal.
 2. The variable waveguideattenuator according to claim 1 wherein said composition processorselectively varies concurrently at least two among said volume, saidloss tangent, said permittivity and said permeability within the atleast one subcavity in response to said waveguide attenuator controlsignal.
 3. The variable waveguide attenuator according to claim 1wherein the waveguide attenuator has an attenuation and said compositionprocessor selectively varies said loss tangent to vary said attenuation.4. The variable waveguide attenuator according to claim 1 wherein thewaveguide attenuator has an attenuation and said composition processorselectively varies said loss tangent to maintain said attenuationconstant as at least one of said permittivity and said permeability isvaried.
 5. The variable waveguide attenuator according to claim 1wherein the waveguide attenuator has a characteristic impedance and saidcomposition processor selectively varies said permeability to maintainsaid characteristic impedance approximately constant when at least oneof said loss tangent, said permittivity, and said volume is varied. 6.The variable waveguide attenuator according to claim 1 wherein thewaveguide attenuator has a characteristic impedance and said compositionprocessor selectively varies said permeability to adjust saidcharacteristic impedance.
 7. The variable waveguide attenuator accordingto claim 1 wherein the waveguide attenuator has a characteristicimpedance and said composition processor selectively varies saidpermittivity to maintain said characteristic impedance approximatelyconstant when at least one of said loss tangent, said permeability, andsaid volume is varied.
 8. The variable waveguide attenuator according toclaim 1 wherein the waveguide attenuator has a characteristic impedanceand said composition processor selectively varies said permittivity toadjust said characteristic impedance.
 9. The variable waveguideattenuator according to claim 1 wherein a plurality of component partsare dynamically mixed together in said composition processor responsiveto said waveguide attenuator control signal to form said fluidicdielectric.
 10. The variable waveguide attenuator according to claim 9wherein said composition processor further comprises a component partseparator adapted for separating said component parts of said fluidicdielectric for subsequent reuse.
 11. The variable waveguide attenuatoraccording to claim 1 wherein said composition processor furthercomprises at least one proportional valve, at least one mixing pump, andat least one conduit for selectively mixing and communicating aplurality of said components of said fluidic dielectric from respectivefluid reservoirs to a waveguide attenuator cavity.
 12. The variablewaveguide attenuator according to claim 1 wherein said fluidicdielectric is comprised of an industrial solvent.
 13. The variablewaveguide attenuator according to claim 14 wherein said industrialsolvent has a suspension of magnetic particles contained therein. 14.The variable waveguide attenuator according to claim 15 wherein saidmagnetic particles are formed of a material selected from the groupconsisting of ferrite, metallic salts, and organo-metallic particles.15. The variable waveguide attenuator according to claim 15 wherein saidcomponent contains between about 50% to 90% magnetic particles byweight.
 16. The variable waveguide attenuator according to claim 1,further comprising a second waveguide filter cavity.
 17. The variablewaveguide attenuator according to claim 16, wherein said secondwaveguide filter cavity is at least partially filled with a secondfluidic dielectric.
 18. The variable waveguide attenuator according toclaim 17, further comprising at least a second composition processoradapted for dynamically changing a composition of said second fluidicdielectric to vary at least one of a volume, a loss tangent, apermittivity and a permeability of said second fluidic dielectric.
 19. Amethod for attenuating an RF signal comprising the steps of: providingat least one waveguide filter cavity within a waveguide; at leastpartially filling said waveguide filter cavity with a fluidicdielectric; propagating said RF signal within said waveguide; anddynamically changing at least one among a volume and a composition ofsaid fluidic dielectric to selectively vary at least one of a losstangent, a permittivity and a permittivity of said fluidic dielectric inresponse to a waveguide attenuator control signal.
 20. The methodaccording to claim 19 further comprising the step of selectively varyingat least two among said loss tangent, said permittivity and saidpermeability concurrently in response to said waveguide attenuatorcontrol signal.
 21. The method according to claim 19 further comprisingthe step of varying said loss tangent to vary said attenuation.
 22. Themethod according to claim 19 further comprising the step of varying saidloss tangent to maintain said attenuation constant as at least one ofsaid permittivity and said permeability is varied.
 23. The methodaccording to claim 19 further comprising the step of selectively varyingsaid permeability to maintain a characteristic impedance of saidwaveguide attenuator approximately constant when at least one of saidloss tangent and said permittivity is varied.
 24. The method accordingto claim 19 further comprising the step of selectively varying saidpermeability to adjust said characteristic impedance.
 25. The methodaccording to claim 19 further comprising the step of selectively varyingsaid permittivity to maintain said characteristic impedanceapproximately constant when at least one of said loss tangent and saidpermeability is varied.
 26. The method according to claim 19 furthercomprising the step of selectively varying said permittivity to adjustsaid characteristic impedance.
 27. The method according to claim 19further comprising the step of dynamically mixing a plurality ofcomponents in response to said waveguide attenuator control signal toproduce said fluidic dielectric.
 28. The method according to claim 27further comprising the step of separating said components into saidcomponent parts for subsequent reuse in forming said fluidic dielectric.29. The method according to claim 27 further comprising the steps ofselectively mixing said components of said fluidic dielectric fromrespective fluid reservoirs.
 30. The method according to claim 19,further comprising the step of providing a second waveguide filtercavity.
 31. The method according to claim 30, further comprising thestep of at least partially filling said second waveguide filter cavitywith a second fluidic dielectric.
 32. The method according to claim 31,further comprising the step of providing at least a second compositionprocessor adapted for dynamically changing a composition of said secondfluidic dielectric to vary at least one of a loss tangent, apermittivity and a permeability of said second fluidic dielectric.